1. Field of the Invention
The present invention relates to a method of lowering the permeability of a Co alloy sputtering target which is used in the formation of a Co alloy film as a recording material in the electric field, and particularly to a method of lowering the permeability of a difficult-to-work Co alloy by introducing working strain.
2. Description of the Related Art
As recording materials used in the electric field, there have been generally used films of Co alloys such as Co-Ni-Pt, Co-Cr-Ni, and Co-Cr-Ta alloys. Recently, these recording materials have been required to be further increased in recording density, and Co alloys capable of satisfying the requirement have been developed mainly by increasing the kinds and amounts of alloy components.
Co alloy targets used in the formation of films require various characteristics, and particularly, they strongly require the lowering in permeability. The lowering in permeability is most effective to enhance the sputtering efficiency of Co alloy targets and it also greatly contributes to the reduction in cost from the viewpoint of users.
In general, to lower the permeability of Co alloy targets, strain is introduced to a Co alloy by cold-working or hot-working, exemplified in Examined Japanese Patent Publication No. HEI 2-49384 and Unexamined Japanese Patent Publication No. SHO 61-257473. This method involves a melting-casting-rolling process, and which is relatively simply applicable for conventional Co alloys excellent in workability without an increase in cost. This method, however, has a difficulty in working Co alloys recently developed or being in the course of development, because these alloys are added with Boron (B) forming a low melting point compound or added with a large amount of a high melting point metal for strengthening the base phase.
From this reason, Co alloy targets have come to be mainly manufactured by a precision casting process or a powder metallurgy process.
The precision casting process has a merit in manufacturing Co alloy targets at a low cost; however, films formed of the Co alloy targets manufactured by this process frequently cause a trouble by arcings during the sputtering due to casting defects. To avoid such inconvenience, the cooling rate during casting must be lowered. However, the lowered cooling rate causes the coarsening of crystal grains, and aggregation and coarsening of precipitations, which makes it difficult to work the Co alloy ingot obtained by this casting, thereby failing to achieve the lowering in permeability.
On the other hand, the powder metallurgy process is effective to form a difficult-to-work material; however, it has a disadvantage in the terms of the increased cost, and therefore, it has been little put in practical use as a method of manufacturing Co alloy targets.